1. Field of the Invention
The present invention relates to an inclination angle sensor, and more particularly, it relates to an inclination angle sensor for detecting an inclination angle from an amount of change of a capacitance.
2. Description of the Related Art
The present invention is directed to an inclination angle sensor, which belongs to a field adjacent to that including a rotation angle sensor. In relation to such a rotation angle sensor, a capacitance type rotation angle sensor which is of interest to the present invention is described in Japanese Utility Model Laying-Open No. 55-88109 (1980), for example.
This rotation angle sensor comprises a plurality of fixed electrodes and a plurality of rotatable electrodes which are positioned between the fixed electrodes, and the rotatable electrodes are mounted on a shaft which is rotatably supported. Respective shapes of the fixed and rotatable electrodes are so selected that overlap areas thereof are varied with change of the rotation angle of the shaft. The shaft is rotated in correspondence to the rotation angle to be detected. Thus, the overlap areas of the fixed and rotatable electrodes are varied in correspondence to the rotation angle to be detected, whereby a capacitance which is formed by these electrodes is changed. This capacitance is taken out by a first terminal which is electrically connected with the fixed electrodes and a second terminal which is electrically connected with the rotatable electrodes. Thus, it is possible to recognize the rotation angle to be detected by change of the capacitance.
The aforementioned electrical connection between the fixed electrodes and the first terminal can be readily attained through a conductive member which is directly mounted on the fixed electrodes. On the other hand, the electrical connection between the rotatable electrodes and the second terminal is attained through a collector or a brush being slidably in contact with the shaft for allowing rotation of the rotatable electrodes, which shaft is made of a conductive material. With respect to rotation of the rotatable electrodes and the shaft, therefore, frictional resistance is caused by the collector or the brush to an unignorable degree.
In order to apply the structure of the aforementioned rotation angle sensor to an inclination angle sensor, therefore, it is necessary to solve the problem of frictional resistance. When the aforementioned rotation angle sensor is employed as an inclination angle sensor, the rotatable electrodes are movably supported so as to regularly face a constant direction with respect to the gravitational direction. However, the gravitational force for making the rotatable electrodes face the constant direction with respect to the gravitational direction is relatively small since the same is substantially provided merely by the gravitational force of the rotatable electrodes themselves. When rotation of the shaft is influenced by the frictional resistance caused by the collector or the brush as described above, therefore, the rotatable electrodes may not correctly face the constant direction with respect to the gravitational direction. Further, such friction may cause wear on the sliding contact portion, resulting in an inferior electrical contact, and hence the life of a sensor depends on the life of the collector or brush. As the result, such an inclination angle sensor deteriorates in reliability with respect to accuracy in measurement of the inclination angle.